In the past, for a variety of reasons, well operators have needed to isolate different zones within the wellbore for production or stimulation reasons. To accomplish isolation of more than one zone within a wellbore, a multi-bore packer has generally been used, wherein two or more tubulars extend through the packer seal and the seal typically surrounds each of the tubulars within the packer housing. When such prior packers are actuated for pack-off against the casing, difficulties have been encountered in getting a complete and reliable seal around each of the tubulars. This is because the sealing element, disposed around each of the tubulars, was difficult to position appropriately so that it could be reliably squeezed radially outwardly for continuous contact with the casing to effect the necessary seal. The seal could be a single element that has bores therethrough so that the various strings can run through the element. However, setting this type of element by the traditional method of sliding sleeves has in the past created concerns about reliability of the seal around each of the strings. This was particularly true with regard to the space in between the strings in a situation where a sleeve compressed the sealing element to obtain the seal against the casing. Typical of such installations is U.S. Pat. No. 3,299,959. Other patents in the area of multiple-completion packers are U.S. Pat. Nos. 4,413,677; 3,224,508; 3,299,959; and 4,413,677. PG,3
Various locking mechanisms preventing longitudinal release have also been employed in the past. These typically involve the use of collets that are supported, followed by the removal of support for the collets by virtue of use of a shifting sleeve. Typical of such designs are U.S. Pat. Nos. 4,624,311; 4,516,634; 4,669,539; 5,180,010; and 5,217,077.
Also of general interest in the area of multi-string packer seals are U.S. Pat. Nos. 3,166,127; 3,211,226; 3,275,079; and 4,852,649.
The problems with prior lock assemblies is that they were mounted internal to the tool and fixed with frangible members such as shear pins. Accordingly, testing the connections as the packer assembly was run in the hole created a hazard that the various frangible members holding the lock mechanisms would shear, prematurely defeating the lock. Additionally, once a lock mechanism actuated, prior designs did not provide a design feature to immobilize the piston of the lock assembly to avoid cycling downhole upon pressure fluctuations experienced by the lock piston. The lock mechanisms of prior designs involved seals such as O-rings which, if retained by components that were subject to back-and-forth cycling upon pressure variations, could jeopardize the seal integrity of the string or strings running through a packer.
Accordingly, the apparatus of the present invention provides for a simple and reliable way to seal multi-string packers involving a unitary external seal, coupled with a plurality of internal seals which can tolerate relative movement. The apparatus is adaptable for two or more strings through a packer housing or hub. Additionally, a lock mechanism, accessible from outside the hub, is provided to facilitate pressure-testing by the rig crew during make-up and run-in into the wellbore. Once actuated to unlock, another feature is provided which retains the locking mechanism in a stationary position to avoid excessive wear on sealing components which could undermine the force exerted on the slips and sealing elements.